Libertinus made a fix for this earlier this year: https://github.com/alerque/libertinus/issues/300 The issue is also resolved in more recent versions of FreeType.
I think this is related to this issue: https://lists.nongnu.org/archive/html/freetype-devel/2018-12/msg00063.html The problem only seems to appear with poppler, so the character is viewable in e.g. webkit or Adobe PDF viewers.